Isomerization of nitriles

ABSTRACT

PROCESS OF ISOMERIZING 2-METHYL-3-BUTENENITRILE TO 3PENTENENTIRIELS AND 3-PENTENENITRIELS TO 4-PENETNEENTITRILE USING A COMPOUND OF COBALT OR RHODIUM IN CONJUNCTION WITH AN OXIDIZING AGENT OR REDUCING AGENT PRESENT IN AN AMOUNT SUCH THAT THE COBALT OR RHODIUM HAS AN EFFECTIVE VALENCE BELOW +2 AND GENERALLY OF FROM 0.25 TO 1.75 AS CATALYST AND OF ADDING HYDROGEN CYANIDE TO CARBON-CARBON DOUBLE BONDS SUCH AS IN 4-PENTENENTITRILE AT FROM -25 TO 200*C. USING THE SAME COBALT OR RHODIUM CATALYST SYSTEM.

United States Patent 3,579,560 ISOMERIZATION 0F NITRILES William Charles Drinkard, Jr., Wilmington, Del., and Brian W. Taylor, Pittsburgh, Pa., assignors to E. I. du Pont de Nemours and Company, Wilmington, Del. No Drawing. Continuation-impart of application Ser. No. 680,969, Nov. 6, 1967. This application Oct. 28, 1968, Ser. No. 771,313

Int. Cl. C07c 121/30 U.S. Cl. 260-4653 20 Claims ABSTRACT OF THE DISCLOSURE Process of isomerizing 2-methyl-3-butenenitrile to 3- pentenenitriles and 3-pentenenitriles to 4-pentenenitrile using a compound of cobalt or rhodium in conjunction with an oxidizing agent or reducing agent present in an amount such that the cobalt or rhodium has an effective valence below +2 and generally of from 0.25 to 1.75 as catalyst and of adding hydrogen cyanide to carbon-carbon double bonds such as in 4-pentenenitrile at from 25 to 200 C. using the same cobalt or rhodium catalyst system.

CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of application Ser. No. 680,969, filed Nov. 6, 1967, by William Charles Drinkard, Jr., and Brian W. Taylor, now abandoned BACKGROUND OF THE INVENTION It is known that the addition of hydrogen cyanide to double bonds adjacent an activating group such as a nitrile or acyloxy group, proceeds with relative ease. However, the addition of hydrogen cyanide to non-activated double bonds proceeds only with difiiculty, if at all, and normally requires the use of high pressures of about 1,000 p.s.i. or more and high temperatures in the range of 200 to 400 C. U.S. Pat. No. 2,666,748, issued Jan. 19, 1954, to Paul Arthur, Jr., and Burt Carlson Pratt, discloses a technique which involves the use of cobalt carbonyl with or without the addition of a tertiary aryl phosphine or arsine. This process suffers from producing a relatively high percentage of undesirable polymeric products when applied to monoolefinic starting materials and a relatively poor yield in all cases. Furthermore, this process is not satisfactory for the production of adiponitrile from 3- or 4-pentenenitrile. The selective formation of 4-pentenenitrile from 3-pentenenitrile without formation of the thermodynamically more stable 2-pentenenitrile is believed to be unknown in the art.

SUMMARY OF THE INVENTION The present invention provides a process or a step in a process which produces nitriles or dinitriles from olefins in high yield under mild conditions, with minimal formation of polymer.

The process of the present invention is generally applicable to unsaturated compounds of from 2 to 20 carbon atoms having at least one aliphatic carbon-carbon double bond. Butadiene, 3-pentenenitrile, 4-pentenenitrile and 2- methyl-3-butenenitrile are especially preferred. Suitable unsaturated compounds include monoolefins and monoice olefins substituted with groups which do not attack the catalyst such as cyano, aldehyde, ester, and ketone.

These unsaturated compounds include diolefins such as butadiene, monoolefins containing from 2 to 20 carbon atoms such as ethylene, propylene, butene-l, pentene-Z, hexene-Z, etc., and substituted compounds such as styrene, 3-pentenenitrile, and 4-pentenenitrile. The process also finds special advantage in the production of 2- methyl-glutaronitrile from 2-methyl-3-butenenitrile.

In the preferred process of the present invention wherein adiponitrile is formed from 3-pentenenitriles or 2-methyl-3-butenenitrile the reaction proceeds in several steps. The first step involves the isomerization of 2-methyl-3- butenenitrile to 3-pentenenitriles. The next step involves the isomerization of 3-pentenenitriles to 4-pentenenitn'le followed by the final step, which involves the addition of hydrogen cyanide to 4-pentenenitrile to form adiponitrile. In this process the 3-pentenenitriles and 2-methyl-3-butenenitrile can be made by the hydrocyanation of butadiene.

The isomerization steps are catalyzed by cobalt or rhodium compounds having a valence of less than +2, generally having an effective valence inv the system of from 0.25 to 1.75, and the hereinbelow defined cobalt or rhodium compounds for catalyzing and the hydrocyanation step.

The catalysts for the hydrocyanation step are cobalt or rhodium compounds wherein at least some of the cobalt or rhodium is believed to have a valence of +1. Such catalysts can readily be prepared from conventional cobalt or rhodium compounds wherein the cobalt or rhodium has a valence of +1 such as HCo[P(C H or 0 such as Co (CO) [POC H 2 such as CoCl or 3 such as RhCl by treating such compound with an appropriate amount of an oxidizing or reducing agent so as to bring the average or eifective valence of the cobalt or rhodium below +2, generally to within the range of +0.25 to +1.75, and preferably within the range of +0.75 to +1.25. The cobalt or rhodium may be supplied to the catalyst system in many forms including coordination compounds of cobalt or rhodium or salts of cobalt or rhodium. Suitable coordination compounds may contain the low valent cobalt or rhodium in conjunction with a sigma/ pi bonding ligand. The compound is then oxidized by a convenient means such as with ferric chloride to form a catalyst of the structure L MX wherein M is selected from the class consisting of Co and Rh, X is an anion and L is a neutral ligand. The ligands useful as L may be defined as any atoms or molecule capable of functioning as a sigma/pi bonded partner in one or more coordinate bonds. A description of such ligands may be found in Advanced Inorganic Chemistry by F. Albert Cotton and G. Wilkinson, published by Interscience Publishers, a division of John Wiley & Sons, 1962, Library of Congress caatalog card No. 62148l8; particularly on pages 602-606. Preferred ligands for use here have the structure Z M' Wherein Z and M have the meanings defined below.

-In the case where the cobalt or rhodium is supplied to the system as a salt or as a +2 or +3 valent complex it is generally necessary to utilize a reducing agent. Convenient reducing agents to use are metals which are sufficiently electronegative to reduce cobalt to C0 or rhodium to Rh+ In a preferred aspect of the invention the cobalt or rhodium salt is reduced with a metal, which metal also serves as a promoter for the catalyst. Such promoters are described below. Suitable cobalt and rhodi um salts generally are the salts of the mineral acids, and lower fatty acids, organic sulfonic acids, acetonylacetonate, fiuoroboric acid and salicaldehyde. Of these, the halides and particularly the chlorides, bromides, and iodides, are preferred because of their availability and simplicity of use.

In a preferred aspect of the invention a phosphite is used to enhance the activity of the catalyst and to control the isomer distribution of the product. This is particularly important in the production of adiponitrile from 3- pentenenitrile or 4-pentenenitrile where a catalyst system such as cobalt chloride and iron gives a product consisting almost entirely of methyl glutaronitrile whereas the same catalyst system when used in conjunction with a phosphite such as triphenyl phosphite can give a product in which 80 percent or more of the dinitriles produced are adiponitrile which normally is the desired product. The prefered phosphites have the structure P(OR) 'Wherein R is an alkyl or aryl radical of up to 18 carbon atoms. Genorally the phosphite is used in a molar ratio of phosphite to cobalt or rhodium of from 0.5 :1 to 12:1 and preferably from 2.5:1 to 4.511.

A preferred class of catalysts are believed to have the structure [(Z) M'] MX wherein Z is selected from the class consisting of OR and R, wherein R is selected from the class consisting of alkyl and aryl groups having up to 18 carbon atoms, M is selected from the class consisting of cobalt and rhodium and X is a halide or CN. These catalysts can be prepared by any of several techniques; for instance, catalysts of the formula (Z M') RhX Wherein Z, M and X have the meanings defined above, are readily prepared by mixing a rhodium halide with an excess of a compound of the formula Z 1 at a moderately elevated temperature such as 100 C. When using the cobalt catalysts, the catalyst can also be prepared in situ by adding the two components to the reaction vessel preferably in substantially equimolar amounts. The HCo(Z M) starting material can be prepared by the technique set forth in Example 55 below. Preferably, these catalyst compounds are prepared by the partial reduction of a cobalt halide with a metal such as zinc or iron in the presence of a compound of the formula Z M' wherein Z and M have the meaning defined above.

The hydrocyanation or isomerization reaction can be carried out with or without a solvent. The solvent should be a liquid at the reaction temperature and inert towards the unsaturated compound and the catalyst. Generally, such solvents are hydrocarbons such as benzene, xylene, or nitriles such as acetonitrile, benzonitrile, or adiponitrile.

The exact temperature used is dependent, to a certain extent, on the particular catalyst being used, the particular unsaturated compound being used and the desired rate. Generally, temperatures of from -25 C. to 200 C. can be used with from C. to 150 C. being the preferred range for both isomerization and hydrocyanation.

Both the isomerization reaction and the hydrocyanation reaction may be carried out by charging a reactor with all of the reactants. Preferably, in the case of hydrocyanation the reactor is charged with the catalyst or catalyst components, the unsaturated compound and whatever solvent is to be used and the hydrogen cyanide gas is swept over the surface of the reaction mixture or bubbled through said reaction mixture. If desired, when using a gaseous unsaturated organic compound, the hydrogen cyanide and the unsaturated organic compound may be fed together into the reaction medium. The molar ratio of unsaturated compound to catalyst generally is varied from about :1 to 2000z1 unsaturated compound to catalyst for a batch operation. In a continuous operation such as when using a fixed bed catalyst type of operation, a much higher proportion of catalyst may be used such as 1:2 unsaturated compound to catalyst.

Optionally, a promoter may be used to activate the catalyst for the hydrocyanation reaction. The promoter generally is a Lewis Acid such as a cationic form of a metal such as zinc, cadmium, beryllium, aluminum, gallium, indium, thallium, titanium, zirconium, hafnium, erbium, germanium, tin, vanadium, niobium, scandium, chromium, molybdenum, tungsten, manganese, rhenium, palladium, thorium, copper, lead and iron. Other suitable promoters are salts of the metals listed above and include aluminum chloride, zinc chloride, cadmium iodide, titanium trichloride, titanium tetrachloride, zinc acetate, ethyl aluminum dichloride, chromic chloride, stannous chloride and zinc iodide. The promoter acts to improve catalyst efiiciency and, in certain cases such as the hydrocyanation of 3- or 4-pentenenitrile to adiponitrile, can result in an improved yield. The preferred promoters are cationic forms of zinc, cadmium, aluminum, indium, zirconium, tin, manganese, calcium, copper, lead, and iron. These metals may 'be supplied to the catalyst system in the form of a salt when using a previously reduced catalyst or in the form of the metal which in the case of an un reduced catalyst in turn serves to reduce the catalyst, as well as to promote the activity of the catalyst. Suitable anions are the halides, especially the chlorides, bromides and iodides, and the lower fatty acids. Preferably, the promoter is formed by the reaction of the metal and the unreduced or incompletely reduced catalyst precursor. Generally, the promoter is used in a molar ratio of cobalt or rhodium to promoter of from 16:1 to 1:16. The pressure used is not critical and may be varied from 0.1 to 10 or more atm. However, it is preferable to keep the partial pressure of HCN in the reactor below about 1 atm.

If desired, an excess of a pi-bouding ligand such as an aryl phosphite may also be added to the reaction mixture.

Preferably, the reaction mixture is agitated, such as by stirring or shaking.

The cyanated product can be recovered by conventional techniques such as crystallization of the product from solution or by distillation.

The nitriles formed by the present invention are useful as chemical intermediates. For instance, adiponitrile is an intermediate used in the production of hexamethylene adipamide, a commercial polyamide, useful in forming fibers, films and molded articles. Other nitriles can be converted to the corresponding acids and amines which are conventional commercial products.

DESCRIPTION OF THE PREFERRED (EMBODIMENTS In each of Examples 1-51, a 50 ml., three-necked, glass, round bottom flask, fitted with a water-cooled reflux condenser connected to a Dry Ice trap, a gas inlet above the liquid level, and a magnetic stirrer is set up in an oil bath maintained at the temperature indicated under Temp. in Table I. The flask is purged with nitrogen gas and charged with the materials indicated in Table I. In Examples 1-3, and 5-50, 20 g. of 3-pentenenitriles is charged to the flask. In Examples 4 and 51, 20 g. of 2-methyl-3-butenenitrile is charged to the flask. A stream of nitrogen gas is bubbled through liquid hydrogen cyanide contained in a 20 ml. glass flask cooled in an ice bath. The resulting gas mixture is swept across the surface of the reaction mixture in the flask. The nitrogen gas flow is adjusted so that the feed rate of HCN (measured as a liquid at 0 C.) is fed to the flask at the rate indicated in Table I. The amounts of ADN (adiponitrile), MGN (Z-methylglutaronitrile), ESN (ethylsuccinonitrile), and 4-PN (4-pentenenitrile) reported in Table I in the product are based on the percentage of the particular nitrile in the crude reaction mixture as determined by gas chromatographic analysis. In Examples 2, 3, 49, and 50, the indicates that the mate rial listed under Reducing Agent is actually an activator and not a reducing agent. In Example 37, Co(OAc) 3 3 c2 3d 505 w: zmo g ovfi om 3 .0 mm .o c mm :3 H o mm d u m m u v v .0 mm AN .0 NH OOH H .C l1 mm .0 :N m .N NAQMOAUOO mm 4o 3 .m 0 am can .H 0 I mm c QN o m NQawvQO l $6 0 $3 0 ma 2: ad 1 Q6 MED .HH AZOVOU n c mm o N d E 2: H o w @H 13...! w d :ODZO m A n o 3 A 3 d a :2 o q 3 18...! a A ZSHOYM w H w 3 2mm Z62 Enos 0 a 25 535 Q3 #5654 ufluoaaoo fimv .5654 unscmioo mv 25084 usuonfioo "oz oaaau 9 EXAMPLE 56 A 50 m1., three-necked round bottom glass flask fitted with a water cooled reflux condenser connected to a Dry Ice trap, a gas inlet above liquid level and a magnetic stirrer is set up in an oil bath maintained at 80 C. The flask is purged with nitrogen gas and charged with 1.3 g. CoCl 6.2 g. P(OC H 0.28 g. iron powder, 10 ml. CH CN and 10 ml.

A stream of nitrogen gas is bubbled through liquid hydrogen cyanide contained in a flask cooled in an ice bath. The resulting gas mixture is swept across the surface of the reaction mixture in the flask. The nitrogen gas flow is adjusted so that about 0.1 ml. per hour of hydrogen cyanide (measured as a liquid. at 0 C.) is fed to the reaction flask. After 23 hours the reaction is shut down.

Gas chromatographic analysis and infrared analysis indicate the hydrocyanation of the carbon-carbon double bond of the ,CHO

EXAMPLE 57 Example 56 is repeated except 10 ml. of

ll H OC C 3 is substituted for the Q CHO of Example 56 and the reaction is shut down after 21 hours. Again, gas chromatographic analysis and infrared analysis indicate the hydrocyanation of the carbon-carbon double bond of the l I COCH EXAMPLE 58 A 50 ml., three-necked round bottom glass flask fitted with a water cooled reflux condenser connected to a Dry Ice trap, a gas inlet above liquid level and a magnetic stirrer is set up in an oil bath maintained at 80 C. The flask is purged with a nitrogen gas and charged with 1.3 g. CoCl 6.2 g. P(OC H 25 ml. allyl cyanide, and 0.28 g. iron powder. A stream of nitrogen gas is bubbled through liquid hydrogen cyanide contained in a flask cooled in an ice bath. The resulting gas mixture is swept across the surface of the reaction mixture in the flask. The nitrogen gas flow is adjusted so that about 0.1 ml. per hour of hydrogen cyanide (measured as a liquid at 0 C.) is fed to the reaction flask. After 21 hours the reaction is shut down.

Gas chromatographic analysis indicates that the crude reaction mixture contains 22.8 percent glutaronitrile.

EXAMPLE 59 A 50 ml., three-necked round bottom glass flask fitted with a water cooled reflux condenser connected to a Dry Ice trap, a gas inlet above liquid level and a magnetic stirrer is set up in an oil bath maintained at C. The flask is purged with nitrogen gas and charged with 1.3 g. CoCl 6.2 g. P(0C H 0.28 g. iron powder, and 25 ml. Z-methyl 3 butenenitrile. A stream of nitrogen gas is bubbled through liquid hydrogen cyanide contained in a flask cooled in an ice bath. The resulting gas mixture is swept across the surface of the reaction mixture in the flask. The nitrogen gas flow is adjusted so that about 0.1 ml. per hour of hydrogen cyanide (measured as a liquid at 0 C.) is fed to the reaction flask. After 21 hours the reaction is shut down.

Gas chromatographic analysis indicates that the crude reaction mixture contains 0.09 percent adiponitrile, 23.2 percent 2-methyl glutaronitrile, and 0 percent ethyl succinonitrile.

EXAMPLE 60 A 50 ml., three-necked round bottom glass flask fitted with a water cooled reflux condenser connected to a Dry Ice trap, a gas inlet above liquid level, and a magnetic stirrer is set up in an oil bath maintained at C. The flask is purged with nitrogen gas and charged with 1.3 g. of CoCl 12.4 g. of P(OC H 0.08 g. of aluminum powder and 25 ml. of 2-methyl-3-butenenitrile (containing 8.32 percent 3-pentenenitrile). The mixture is heated at C. for 9 hours. At the end of this time, gas chromatographic analysis shows that the liquid sample contains 17.3 percent 3-pentenenitrile.

EXAMPLE 61 A reaction identical to Example 60, except aluminum powder is replaced with 0.33 g. of zinc powder, is run. At the end of the reaction, gas chromatographic analysis shows that 3-pentenenitrile concentration has increased to 16.1 percent.

EXAMPLE 62 A reaction similar to Example 60 is run using 1.3 g. of C001 9.3 g. of P(OC H 0.33 g. of zinc powder and 25 ml. of 2-methyl-3-butenenitrile. The mixture is heated at 130 C. for 9 hours. At the end of the reaction, gas chromatographic analysis shows that 3-pentenenitrile concentration has increased to 17.3 percent.

We claim:

1. A process of isomerizing 3-penteuenitrile to 4- pentenenitrile comprising feeding a reactor with 3-pentenenitrile and a compound of a metal M wherein M is selected from the class consisting of cobalt and rhodium and an oxidizing agent or reducing agent in an amount sufficient to bring the effective valence of M to from 0.25 to 1.75, while maintaining the contents of said reactor at from -25 to 200 C., whereby 4-pentenenitrile is for-med.

2. The process of claim 1 wherein the compound is a cobalt compound.

3. The process of claim 2 wherein the cobalt compound has the structure Z MCoX wherein Z is selected from the class consisting of R and OR where R is selected from the class consisting of alkyl and aryl groups having up to 18 carbon atoms, and wherein M is selected from the class consisting of P, As and Sb and wherein X is a halide or CN.

4. The process of claim 1 wherein the catalytic metal compound is a rhodium compound.

5. The process of claim 4 wherein the rhodium compound has the structure (Z M') RhX wherein Z is selected from the class consisting of R and OR and wherein R is selected from the class consisting of alkyl and aryl groups having up to 18 carbon atoms, and wherein M is selected from the class consisting of P, As and Sb, and wherein X is selected from the class consisting of halide and CN.

6. The process of claim wherein M is P.

7. The process of claim 6 wherein Z is R.

8. The process of claim 6 wherein R is aryl.

9. The process of claim 2 wherein the cobalt compound is formed by charging the reactor with a compound of the formula CoX wherein X is a halide, and a compound of the structure HCo(MZ wherein Z is selected irom the class consisting of OR and R, wherein R is selected from the class consisting of alkyl groups and aryl groups having up to 18 carbon atoms and wherein M is selected from the class consisting of P, As and Sb.

10. The process of claim 9 wherein M is P.

11. The process of claim 10 wherein X is Cl.

12. The process of claim 11 wherein Z is OR.

13. The process of claim 12 wherein R is aryl.

14. A process of isomerizing 2-methyl-3-butenenitrile to 3-pentenenitrile comprising feeding a reactor with 2- methyl-3-butenenitrile and a compound of a metal M wherein M is selected from the class consisting of cobalt and rhodium and an oxidizing agent or reducing agent in an amount sufficient to bring the effective valence of M to from 0.25 to 1.75 while maintaining the contents of said reactor at from '25 to 200 0, whereby 3-pentenenitrile is formed.

15. The process of claim 14 wherein the compound is a cobalt compound.

16. The process of claim 15 wherein the cobalt cornpound is formed by charging the reactor with a compound of the formula CoX wherein X is a halide, and a compound of the structure HCo(M'Z wherein Z is selected from the class consisting of OR and R, wherein R is selected from the class consisting of alkyl groups and aryl groups having up to 18 carbon atoms and wherein M is selected from the class consisting of P, As and Sb.

17. The process of claim 16 wherein M is P.

18. The process of claim 17 wherein X is Cl.

19. The process of claim 18 wherein Z is OR.

20. The process of claim 19 wherein R is aryl.

References Cited UNITED STATES PATENTS 2,451,386 10/1948 Hager 260-465.8

JOSEPH P. BRUST, Primary Examiner US. Cl. X.R. 

